1. Field of the Invention
This invention relates generally to a waste treatment system and method. More particularly, this invention relates to a plasma torch-jet used for treatment of liquid and gas waste by the high temperature produced from the plasma torch-jet and and the breaking of chemical bonds through collisions of the electrons with the molecules thus decomposing the wastes into atoms or simple molecules.
2. Description of the Prior Art
The need for waste treatment in the hospitals, laboratories in a school or research institute, or the small factories are often small in scale and intermittent. When the liquid waste can not be properly treated by waste water treatment processes, it is usually stored over a prolong period of time until large quantity is accumulated for large scale treatment by a furnace or other appropriate processes. Such arrangement not only requires the use of more limited and often valuable space but also increases the difficulties and procedural complexity in liquid waste collection, storage, safety, transportation and often may impact the operation procedures of different instruments.
The application of the plasma technology to waste treatment, especially for high temperature processing of the toxic waste is well known. The theory and practice for generating plasma of high temperature over 10,000.degree. C. by the use of electric arc over spaced electrodes have been disclosed in many previous U.S. Patents and need not be repeatedly described here in this application.
Chang et al. disclose in U.S. Pat. No. 4,886,001 entitled "Method and Apparatus for Plasma Pyrolysis of Liquid Waste" (issued on Dec. 12, 1989) a method and apparatus for pyrolytically decomposing waste material by injecting a mixture of waste and water or solvent into a plasma torch. The waste material is fed into the torch at an inlet together with a solvent which is fed via another inlet. The waste material mixed with the solvent is then processed in the plasma chamber near the plasma arc. A recombination chamber and scrubber are then used to further process the product gas and particulates generated by the high temperature plasma treatment.
Since Chang's method involves the mixing of the pre-processed waste material with the plasma process-gas, a pre-mixing with special solvent with certain ratios are required. Such process is more complex, requires special technical expertise and suitable only for larger scale operation. As pointed out by Chang et al., the advantage of the patented invention is to increase the feed throughput which are typically required for a central waste process station. Therefore, the invention of Chang et al. does not address the need and resolve the major design considerations of a small scale waste treatment system.
Kulkarni discloses in another U.S. Pat. No. 4,896,614 entitled "Method and Apparatus for Treatment of Hazardous Waste in Absence of Oxygen" a plasma waste treatment system wherein the hazardous waste is transported from a waste stockfeed to the plasma gun through a separate feed line. The plasma gun comprises an enclosed inner tube which is about seven to eight feet high wherein the high temperature plasma arc is generated. The waste material is fed into the inner tube for high temperature treatment. Kilkarni's apparatus is again designed for large scale operation. The system is maintained at high pressure and high temperature with complex piping system and control valves for treatment of large quantity of waste stock-piles.
Pineau et. al disclose in an U.S. Pat. No. 4,980,092 entitled `Method for the Destruction of Chemically Stable Waste` a method for the destruction of chemically stable waste by pyrolysis utilizing at least one plasma torch. The waste generated inside a duct having an end orifice flows upward passing the orifice directing toward the nozzle of the plasma torch. The axis of the nozzle of the plasma torch and the axis of the orifice are substantially co-linear. The purpose is to precisely inject the gaseous or liquid waste to the high temperature zone of the plasma torch. However, for a small scale and non-continuous infrequent operation, the process to align the axis of the nozzle of the plasma torch to be co-linear with the axis of the orifice may be time consuming and requires special instruments. Additionally, unless the co-linear configuration can be securely maintained by other fixtures, the efficiency of the waste disposal may be greatly reduced if there is a displacement of orifice away from the nozzle of the plasma torch.
One major difficulty in applying the prior art technology to small scale liquid and waste treatment is that the waste material is introduced into the plasma torch area without precise control. When attempts are made to control, e.g., the invention as disclosed by Pineau et. al, the system may require additional operational processes by use of additional instruments which often render the system unsuitable for small scale operation.
Furthermore, the waste material in the larger waste treatment system is prevented from contacting the electrodes because of the larger size of the plasma torch. Also, the concern of maintaining and cleaning the electrodes is not a limitation in the prior applications because regular cleaning-up and maintenance of the electrodes by technical specialists are part of routine operational procedure for a central waste treatment station or larger plasma waste process reactors. This operation routine however may not be feasible for a low cost, small scale laboratory operation. There is still a need in the art of using the plasma torch for waste treatment to precisely control the injection of the waste to the plasma torch in order to overcome this limitation.
Therefore, for those skilled in the art, the need still exists for a waste treatment system which is small, easy to use, and can be operated near where small amount of liquid or gas waste is generated in an effective manner. Such system must also apply a technique capable of precisely controlling the injection of the waste to the plasma torch thus preventing direct contact of the waste material with the electrodes thereby the electrodes may be maintained clean continuously without requiring frequent service.